New solar project

[daveyboy12]

I have a 30 foot travel trailer with plenty of space on the roof and I want to do some remote camping. I'd like to be able to run the refrigerator, watch TV through-out the day, and be able to use laptop, and some other small electrical items.

I was planning on getting two of the Grape 250 watt mono panels. I've heard others say the MC4 connectors don't work all that well so they cut the MC4 off and splice in 10 or 8 AWG. I know this likely voids the panel warranty. Either way, I would fish the two sets of wires down an existing vent (refrigerator vent likely). Down into the lower storage bay.
There I planned on buying a decent charge controller, something I could use on another project down the road, the midnite classic 150. I would likely install a breaker/shut off box (as smkettners install).

I am thinking I could get 8 six volt trojans (T-105) batteries with a 1500w or 2000w inverter.

I was even thinking about installing a 30 amp transfer switch, wiring the inverter into the 'generator input' and taking the existing 30 amp shore power plug, wiring that into the 'shore input'. Then wiring the transfer switch output to the existing shore power input. That should give me power to the entire trailer??? I don't think I could run the microwave and everything, but that would allow me to use any receptacle.

Does anyone have any suggestions?

[JiminDenver]

Toss around a 8-D a few times and you'll think those L16's are light. lol

[mena661]

Almot wrote:

Trojan L16 weight: 125 lbs. I wouldn't try lifting it on my own.

Mine are 370Ah which are 100 lbs. Use your legs not your back. Besides, with a well designed battery tray these should only be lifted once and that's to get them into the tray. I really don't understand why lifting is a concern. Leave the batteries in the rig.

[Almot]

daveyboy12 wrote:
How do you best determine your battery level charge?

What 2oldman said. Keep in mind that those voltages are for RESTED battery, i.e. 24(?) hours after the end of charging and in absence of loads. Practically, it's close enough if you measure voltage in the morning, before solar kicks in and without high-draw devices running.

daveyboy12 wrote:
Do they make a battery charge level meter?

No. There are standalone meters like Trimetric, or sometimes there is capacity-measuring feature on solar controller display, they calculate capacity from the net AH flow, but you can't rely on them. High loads will screw the readings up, not to mention directly wired inverter. The only accurate measuring is specific gravity (not applicable to AGM), or voltage at rest.

And there is also an "idiot green light" 🙂 - green indicator on solar controllers without display. It tells you when the battery is near full. God only knows exactly when it lights up - supposedly at ~90%. I prefer seeing the voltage.

Trojan L16 weight: 125 lbs. I wouldn't try lifting it on my own.

[mena661]

daveyboy12 wrote:
How do you best determine your battery level charge? If I fully charge them, how would I know they are at 75% or 50%? Does the voltage drop to say 6 volts when they are 50% CHARGED? Do they make a battery charge level meter?

You would wire 4 6V's in series/parallel so that they'll still be 12V so you can use the 12V charge tables. Honestly, with 740 amp hours of batteries I only occasionally check my battery monitor just to either make sure everything is working ok or for nerd purposes. 🙂 I pretty much use as much power as I like on a 3-4 day trip. I had these in my old 5th wheel too and with the extremely low parasitic draw in that rig, I never went below 80% SOC even on a 4 day trip.

Old rig - batteries in front storage compartment

[mena661]

Almot wrote:
One little problem is that it takes two big guys to lift one L16.

I lift them by myself and I'm not big at all but it's just from the tray to the ground and vice versa. Once I get a reinforced tray and longer slides then I won't have to lift them at all.

[CA_Traveler]

Google Trimetric 2025 for a decent battery monitor.

[time2roll]

The 12 Volt Side of Life

[2oldman]

From a google search of '6v battery charge table':


100% 6.3
75% 6.2
50% 6.1
25% 6.0

[daveyboy12]

How do you best determine your battery level charge? If I fully charge them, how would I know they are at 75% or 50%? Does the voltage drop to say 6 volts when they are 50% CHARGED? Do they make a battery charge level meter?

[ktmrfs]

mena661 wrote:
Like others have said, unless you're running a MW, coffee maker or other high draw appliance, a 300W inverter and two GC's will be plenty. And I wouldn't even bother with more than a 200-250W panel either. IMO, if you want to pig out on power but not use the high draw stuff, get four 435Ah L16's instead of the 8 GC's. The L16's weigh less overall and take up less space. Yes, you'll lose some amp hours and they're taller than GC's but I have 4 of the 370Ah versions and have plenty of power. No solar either.

good advice. I have 160W of portable solar and I use 4 T-125GC with a 1000W inverter for the microwave etc. (Panasonic true inverter, so I can set it for max power of 800VA easily).

I'd have use L-16's but couldn't manage the height and they are heavy. But if you can fit them in by all means use L-16's instead of GC.

We are prudent, but not anal about power when we dry camp. microwave occasionally, DW uses hair dryer, use maxair vent fans when hot, furnace when cold and LED lights. use lights in the AM and evening. Even with all that we can go at least 8 days before the battery bank is down to 50%SOC with 4 GC with 6hours of solar/day. (Darn Trees and mountains, kill the # solar hours in the fall.)

[Almot]

With 4*L16 and no high-draw stuff they could dry-camp 7-8 days without any solar, and 250W panel would extend the stay to 2 weeks.

The total weight would be the same as 8*GC, the total fumes also the same, total space - probably less. One little problem is that it takes two big guys to lift one L16.

[mena661]

Like others have said, unless you're running a MW, coffee maker or other high draw appliance, a 300W inverter and two GC's will be plenty. And I wouldn't even bother with more than a 200-250W panel either. IMO, if you want to pig out on power but not use the high draw stuff, get four 435Ah L16's instead of the 8 GC's. The L16's weigh less overall and take up less space. Yes, you'll lose some amp hours and they're taller than GC's but I have 4 of the 370Ah versions and have plenty of power. No solar either.

[Almot]

I think - AGM. For 500W it's 4*100 AH @12V, or at least 4*90.

Their plans to put 8 (!!) GC in a storage compartment of travel trailer sound scary. Sliding tray is one pain, reinforcing the bottom is another. Somebody on that list of projects did this - welded an extra I-beam underneath the frame. And then yet another pain - literally - acid fumes from 8 batteries in the trailer.

With power hungry (=current heavy) items like MW, coffee maker, toaster etc (in other words, things that you could live without, if it's just one week), they would need 4 GC or 12V equivalent in AH. With only 2 GC, the current will be high per cell, and 250 AH leave zero margin for when it rains.

Then again, their generator plans are not clear, and neither is energy consumption pattern, i.e. all those not mentioned "other small electrical items". Those that they did mention - TV, laptop etc - don't consume much. 2 GC with 500W panel could work IF there are no high-current items and/or there is a genny for backup. And then there are plans of adding more panel wattage - how much more? Too many variables to suggest anything...

[2oldman]

daveyboy12 wrote:
How much maintenance are we talking about with the batteries, typically? What is a good GEL battery for solar. Do they have a decent life?

The maintenance and weight of my 6 Trojans drove me nuts.

Water once maybe twice a month which is a pain with 18 cells to deal with. I bought some water miser caps (those yellow ones) which worked - for about a year. My batteries were on a slide out tray which had to be reinforced and I had to support it with a board to boot. Plus they never get fully charged - that's just too many Ah for my 800w of solar.

You don't want a GEL battery, you want AGM. I'd look at Deka.